This chapter provides a summary of recent psychologically relevant research that has used nonlinear dynamical system concepts. The research discussed covers a variety of applications ranging from studies of psychomotor skill, and perceptual and decision processes to cognitive development and human prediction processes. A consequence of psychopathology being chaotic is that it is difficult to attribute a direct causal effect to environmental events on behavior. The power spectrum was transformed to log-log coordinates and two intersecting lines were fit to each plot, one line having a zero slope to represent the noise region of the spectrum at high frequencies. Ehlers suggested that alcohol may generate its deleterious effects on behavior by producing more chaotic behavior at small dosages but possibly generating limit cycle behavior at large dosages. By applying nonlinear dynamical techniques to analyze data from a variety of psychologically relevant applications, it has been shown how nonlinear tools allow behavioral phenomena to be interpreted in a new light.